The present invention relates to an image pick-up device used for a camera, and in particular, to a solid-state image pick-up device suitable for a thin camera unit that is housed in a mobile terminal.
A small and thin image pick-up device has come to be housed in a small and thin electronic equipment such as a cellphone and PDA (Personal Digital Assistant). Owing to this, it has become possible to transmit not only voice information but also image information mutually to a remote place.
As an image sensor to be used in these image pick-up devices, there are used solid-state image sensors such as a CCD (Charge Coupled Device) type image sensor and a CMOS (Complementary Metal-Oxide Semiconductor) type image sensor.
In these image sensors, some ways are devised by forming a micro-lens on each light-receiving pixel to compensate for a fall of sensitivity caused by reduction of an area of light-receiving pixels resulted from downsizing and higher number of pixels.
On the other hand the image pick-up device stated above is required to be extremely thin because of a tendency of the equipment to be housed to be thin, and it is difficult to meet this requirement if conventional ceramic packages or resin mold packages are used. Therefore, it has been general to make the image pick-up device to be small in size and to be thin in thickness by packaging a semiconductor image sensor chip on which a micro-lens is formed, as it is, in a printed-circuit board constituting an image pick-up device, and then, by assembling an optical system to unite it.
In this case, if dust sticks to the micro-lens in the course of the process, rays of light to a light-receiving pixel are intercepted, causing sometimes problems that image data of a subject are interfered.
For this problem, there is proposed a solid-state image pick-up device wherein an image sensor is packaged while it is kept to be thin.
As examples for this, there are disclosed a solid-state image pick-up device wherein a layer whose refractive index is lower than that of a micro-lens is formed on a micro-lens array, and a transparent plate is arranged on the layer having the low refractive index, and a solid-state image pick-up device wherein a transparent plate is arranged on a micro-lens array through a spacer, and a space between the micro-lens array and the transparent plate is made to be an air layer (for example, see Patent Document 1).
(Patent Document 1) TOKKAI No. 2003-31782
The solid-state image pick-up device described in the Patent Document 1 has an advantage that dust does not stick to a micro-lens even when various processes have passed, and even when dust sticks to a transparent plate, the dust can be wiped off easily, because a micro-lens array portion is covered by the transparent plate for the period from the initial stage of the process to the completion of the image pick-up device, to be isolated from the open air.
However, in the method to form a layer having a low refractive index on a micro-lens array, there are problems that a layer thickness control for the layer having a low refractive index is difficult, and a process to form a layer having a low refractive index needs to be added, resulting in cost increase.
In the method to arrange a transparent plate on a micro-lens array through a spacer, a process to form a spacer, or a spacer member and incorporating thereof need to be added, and a similar cost increase is caused accordingly, which is a problem.